This invention relates to a process for the recovery of manganese from silicateous ores containing the same. More particularly, this invention relates to an improved process for preparing manganese obtained from ocean nodules in a form suitable for steel manufacture without having to highly purify the same. Still more particularly, this invention relates to a method for recovering such metals as zinc, copper, cobalt, nickel and the like from manganese-containing ocean nodule ores containing the same by controlled acid leaching.
U.S. Pat. No. 4,026,773, issued May 31, 1977, teaches one method for separating, recovering and purifying a mixture of metals found in manganiferous ocean nodule ores, e.g. iron, nickel, copper, zinc and the like which are found together in insoluble oxide, or silicate form or the like together with substantial amounts of manganese oxide.
In general, the method taught involves leaching various metals from ocean nodule ores with concentrated HCl at a pH of about -1 to form their soluble chloride counterparts, including MnCl.sub.2, together with released chlorine gas, and thereafter sequentially separating each of the zinc, copper, nickel chlorides etc. from the leach solution, until there remains the MnCl.sub.2, which comprises the largest proportion of the overall metals in the original ore. The MnCl.sub.2 is then reconverted to manganese oxide by chlorine oxidation or the like, for industrial use. Thus, in accordance with this method, the manganese, although it is the largest component, is carried through each of the sequential separation steps as MnCl.sub.2 until all of the other metals are first removed. Necessarily, then, much larger manufacturing facilities, and greater amounts of reagents and energy are required by this method than would be the case if all the metals other than manganese were separated from the ore first without it being necessary to convert manganese oxide to MnCl.sub.2, carry it through the process, and then convert it back again to manganese oxide by oxidation. Moreover, inasmuch as the manganese to be used in steel manufacturing need not be as highly refined as this process provides, this prior art process results in a material which is purer than what is necessary.
In "The Processing of Manganese Nodules by Acid Leaching", W. H. Ulrich et al, INTEROCEAN '73, Second International Conference with Exhibition for Marine Research and Ocean Utilization, Vol. 1, it is disclosed that by leaching nodule ores with HCl or H.sub.2 SO.sub.4 at temperatures between 200.degree. to 250.degree. C. in the presence of steam, copper and nickel could be selectively extracted, and that manganese extraction could be decreased with increasing temperatures. The use of these high temperatures and steam necessarily make such a process very energy-costly.